PhD Candidate: Allix Baxter
Defence date: 25-09-2023
Time: 12:15 – 13:00
Institute: Utrecht University
Location: Utrecht University Hall, Domplein 29, Utrecht
prof. dr. ir. Jaap Sinninghe Damste
prof. dr. Dirk Verschuren
dr. ir. Francien Peterse
Title thesis: Reconstruction of late Quaternary climate in eastern equatorial Africa: Calibration, validation and application of tetraether membrane lipid proxies
As climate scientists try to provide the most accurate forecasts of how Earth’s climate system will change in the future with global warming, information about how different climate variables (like temperature and rainfall) interacted in the past can provide context to current trends and help improve the climate models used to make predictions. In the absence of instrumental weather data before the last century, paleoclimatologists use climate ‘proxies’, types of physical material which can be preserved for long periods and indicative of certain environmental conditions in the past.
This thesis tests and applies climate proxies to 250,000 years of sediments from Lake Chala in equatorial East Africa in order to reconstruct how temperature and the hydrological cycle changed in the Horn of Africa region. The particular proxies used are based on fossil molecules that formed part of the membrane of archaea and bacteria. These organisms can adjust the chemical composition of their membranes to better survive in different lake environments. Moreover, certain archaeal and bacterial species occupy specific niches in lakes. Hence, the diversity of these molecules throughout a lake-sediment archive can reveal past climatic changes.
To ensure that the assumptions about what these proxies represent are trustworthy, this thesis looks in detail at the climate-proxy relationships in the modern-lake system. Additionally, the long-term stability of these relationships is important for correct use of these proxies. Therefore, the timing of when the water column of Lake Chala became stable and similar to that of the present-day lake as the crater basin filled up with sediments is also investigated here. The resulting climate records cover the last 170,000 years, and will likely become important records for climatologists to help improve long-term climate prediction in tropical regions.